The need for better and more reliable systems of water treatment has been a historical challenge. In modern industry, the basic need for clean water and the need to comply with regulations have become increasingly challenging when applied to sources which may contain a variety of dilute pollutants that vary significantly over time. Storm water, for instance, has greater challenges because it is often undesirable to use any form of chemical treatment in a waste stream that may be discharged directly to surface water.
In addition to traditional pollutants such as heavy metals, toxic organics and nutrients, suspended solids are difficult to manage by traditional means and traditional water treatment systems. Suspended solids often comprise particles too small for media filters and particles with neutrally repulsive surface charges, such as those found on finely divided silica clays. Electrocoagulation has been used for a long time, but requires high power consumption and high capital expense. Chitosan and other flocculants are effective on some pollutants, but excessive use of such material may be toxic to fish or other aquatic and/or marine species.